1. Field of the Invention
The present invention relates to a system and method for judging a paper-jam condition in a device such as an image forming apparatus, and more specifically, to a method for judging a paper-jam condition in an image forming apparatus without using a mechanical element such as an actuator and an optical sensor on a discharging side of the apparatus.
2. Description of the Related Art
Generally, an image forming apparatus such as a copier, a printer, and a facsimile, develops an electrostatic latent image which is formed on a photoconductive drum by a laser beam scan of a laser scanning unit (LSU), with a toner to form a visible image. The apparatus then transfers the visible image onto a printing paper and prints an expected image. The image forming apparatus can also judge a paper jam condition when the printing paper is not delivered normally within a system. If so, the image forming apparatus aborts the printing operation so as to allow removal of the paper jam.
FIG. 1 is a view in partial cross section showing a conventional electrophotographic image forming apparatus, and FIG. 2 is a view in partial cross section showing a sensor unit used in the image forming apparatus of FIG. 1. FIG. 3 is a flowchart showing a method for checking the paper jam condition of the image forming apparatus of FIG. 1.
As shown in FIG. 1, to judge the paper jam condition, the image forming apparatus comprises a pickup sensor unit 10 disposed at an upper portion of a paper cassette 1, a feed sensor unit 20 disposed between a photoconductive drum 3 and a fuser 50, and a discharge sensor unit 30 disposed between the fuser 50 and the discharge.
As describe in the flow chart of FIG. 3, the pickup sensor unit 10, which is disposed at the upper portion of the paper cassette 1, judges whether the printing papers are stacked up or not at step S10. In receiving a print order to a printing system, if the pickup sensor unit 10 is in an “ON” state, which means the printing papers are stacked up, a printing mode is continued at step S20. If the pickup sensor unit 10 is in an “OFF” state, meaning that the printing papers are not stacked up, the printing mode is aborted and a user is notified that there is no printing paper at step S50.
In the example where the pickup sensor unit 10 is in the “ON” state, the printing paper is delivered toward an image forming unit, such as through a transfer nip between the photoconductive drum 3 and a transfer roller 7. On the delivered printing paper, a toner image is formed by processes that are well known to those skilled in the art, such as charging, laser beam scanning, developing and transferring. The printing paper is then delivered toward the fuser 50 by a rotatory force of a feeding roller.
At this time, when a leading edge of the printing paper passes the feed sensor unit 20, the feed sensor unit 20 is switched to an “ON” state, and after a predetermined time, if the rear edge of the printing paper safely passes the feed sensor unit 20, the feed sensor unit 20 is switched to an “OFF” state. As the printing paper is delivered toward the fuser 50, the toner image is fixed on the printing paper by a heating roller 50a and a pressure roller 50b. The printing paper on which the toner image is fixed is finally discharged from of the image forming apparatus by a discharge roller 9. Reference numeral 11 indicates a feeding roller, 13 indicates a developing roller and P indicates the printing paper included in FIG. 1.
Returning to FIG. 3, if the feed sensor unit 20 does not switch to the “ON” state after a predetermined time, or is not switched to the “OFF” state after a predetermined time, a control unit judges that the printing paper was delivered abnormally at step S30. Accordingly, the control unit aborts the printing operation and notifies the user of the occurrence of the paper jam at step S60.
If the leading edge of the printing paper, which passed through the fuser 50, then passes the discharge sensor unit 30, the discharge sensor unit 30 is switched to an “ON” state. After a predetermined time, if the rear edge of the printing paper passes the discharge sensor unit 30 and the printing operation is proceeding normally, the discharge sensor unit 30 is switched to an “OFF” state. If the discharge sensor unit 30 does not switch to the “ON” state after a predetermined time, or does not switch to the “OFF” state from the “ON” state after a predetermined time at step S40, it is judged that the printing paper was delivered abnormally and the printing operation is aborted and the user is notified of the occurrence of the paper jam at step S70.
A well-known actuator and a photo interrupter can be used for the feed sensor unit 20 and the discharge sensor unit 30 in FIG. 1. FIG. 2 shows an actuator/interrupter component including an actuator 31 and an optical sensor 33 commonly used for such a feed sensor unit 20 and the discharge sensor unit 30, which will be described in greater detail below.
The actuators 31 of the discharge sensor unit 30 are rotated by the leading edge of the delivered printing paper P. Hence, a phototransistor of the optical sensor 33 receives a light transmitted from a light emitting diode and a sensing signal is generated. Then, the discharge sensor unit 30 is switched to the “ON” state and the control unit detects ingress of the printing paper based on the sensing signal received from the discharge sensor unit 30. After the printing paper passes the actuators 31, the actuators 31 rotate to their initial positions so that the light received to the phototransistor of the optical sensor 33 is blocked off. Therefore, the sensing signal is not generated so that the discharge sensor unit 30 is switched to the “OFF” state and the control unit detects that the printing paper has normally passed through based on the sensing signal received from the discharge sensor unit 30. Though an operation of the feed sensor unit 20 has not been described, interaction of an actuator and an optical sensor of the feed sensor unit 20 thereof is identical with that of the discharge sensor unit 30.
However, in the method for judging the paper jam of the conventional image forming apparatus as described above, the actuator 31 and the optical sensor 33 have to be equipped on a discharging side of the image forming apparatus. Accordingly, the paper jam may be caused by problems of the apparatus, such as an inferior assembly of the actuator 31 and shaping of unit parts. Further, other parts or circuits cannot be installed within an operational range of the actuator 31 due to spatial constraints. In addition, owing to an inferior assembly of the optical sensor 33, the sensing operation may not be performed normally, and owing to a ripple or bounce in the operation of the actuator 31, accurate signal data may not be generated.
Accordingly a need exists for a system and method to judge a paper jam condition in an image forming apparatus without requiring a mechanical element such as an actuator and an optical sensor on a discharging side of the apparatus which are subject to assembly and operational malfunctions.